The present invention relates to a pharmaceutical composition in the form of tablets or capsules which provides a combination of spatial and temporal control of drug delivery to a patient for effective therapeutic results. The pharmaceutical composition comprises an active ingredient or drug, a gas generating component, a swelling agent, a viscolyzing agent, and optionally a gelling polymer. The swelling agent belongs to a class of highly absorbent compounds commonly referred to as superdisintegrants. This class of compounds includes, for example, cross-linked polyvinyl pyrrolidone and cross-linked sodium carboxymethylcellulose. The viscolyzing agent is a highly viscous material which upon contact with gastric fluid entraps the gas produced by the gas generating component. The viscolyzing agent consists of, for example, a carbohydrate gum. The gelling polymer is preferably a cross-linkable gelling polymer, such as a water soluble salt of one or more polyuronic acids, e.g., sodium alginate.
The improved controlled drug delivery system of the present invention is designed to deliver effectively a drug to a patient over a specific time period (temporal control) and from a particular portion of the patient's gastrointestinal tract (spatial control). The improved controlled drug delivery system avoids dose dumping and results in the most therapeutic administration of a particular drug to a person with a particular ailment.
It is well known to those skilled in the art that for ailments requiring multiple doses of a particular drug, the blood levels of a drug need to be maintained above its minimum effective level and below its minimum toxic level in order to obtain the desired therapeutic effects, to avoid undesired toxic effects, and to minimize side effects. When the blood levels of a drug are in this range, the drug is eliminated from the body at a particular rate. A controlled drug delivery system is usually designed to deliver the drug at this particular rate; safe and effective blood levels are maintained for a period as long as the system continues to deliver the drug at this rate. Controlled drug delivery usually results in substantially constant blood levels of the active ingredient as compared to the uncontrolled fluctuations observed when multiple doses of quick releasing conventional dosage forms are administered to a patient. Controlled drug delivery results in optimum therapy, and not only reduces the frequency of dosing, but may also reduce the severity and frequency of side effects.
The above basic concepts of controlled drug delivery are well known to those skilled in the art. Considerable efforts have been made in the last decades to develop new pharmaceutically viable and therapeutically effective controlled drug delivery systems. Attention has been focused particularly on orally administered controlled drug delivery systems because of the ease of administration via the oral route as well as the ease and economy of manufacture of oral dosage forms such as tablets and capsules. A number of different oral controlled drug delivery systems based on different release mechanisms have been developed. These oral controlled drug delivery systems are based on different modes of operation and have been variously named, for example, as dissolution controlled systems, diffusion controlled systems, ion-exchange resins, osmotically controlled systems, erodible matrix systems, pH-independent formulations, swelling controlled systems, and the like.
An orally administered controlled drug delivery system encounters a wide range of highly variable conditions, such as pH, agitation intensity, and composition of the gastrointestinal fluids as it passes down the gastrointestinal tract. Ideally, an oral controlled drug delivery system will deliver the drug at a constant and reproducible rate in spite of the varying conditions. Considerable efforts have therefore been made to design oral controlled drug delivery systems that overcome these drawbacks and deliver the drug at a constant rate as it passes down the gastrointestinal tract.
It is well known to those skilled in the art that a drug may not be absorbed uniformly over the length of the gastrointestinal tract, and that drug absorption from the colon is usually erratic and inefficient. Also, certain drugs are absorbed only from the stomach or the upper parts of the small intestine. Furthermore, an important factor which may adversely affect the performance of an oral controlled drug delivery system is that the dosage form may be rapidly transported from more absorptive upper regions of the intestine to lower regions where the drug is less well absorbed. Therefore, in instances where the drug is not absorbed uniformly over the gastrointestinal tract, the rate of drug absorption may not be constant in spite of the drug delivery system delivering the drug at a constant rate into the gastrointestinal fluids. More particularly, in instances where a drug has a clear cut "absorption window," i.e., the drug is absorbed only from specific regions of the stomach or upper parts of the small intestine, it may not be completely absorbed when administered in the form of a typical oral controlled drug delivery system. It is apparent that for a drug having such an "absorption window," an effective oral controlled drug delivery system should be designed not only to deliver the drug at a controlled rate, but also to retain the drug in the upper parts of the gastrointestinal tract for a long period of time.
An oral controlled drug delivery system is described by Stockwell, A. F., et al., in Journal Controlled Release, 3, 167-175 (1986), who disclosed a hydrocolloid calcium gelled alginate formulation which includes sodium bicarbonate. This composition was investigated by Ingani et al., in Int. J. Pharm., 35, 157-164 (1987), who found that the bioavailability of riboflavin was increased as compared to a standard system. However, it is known that the use of alginate alone presents difficulties in tabletting, film coating, and storage.
U.S. Pat. No. 4,777,033, assigned to Teijin Limited, discloses an oral controlled release pharmaceutical composition comprising a lower alkyl ether of cellulose, polyacrylic acid or its pharmaceutically acceptable salt, a drug, and an effective amount of an effervescent foaming agent. The composition is intended to be retained in the stomach for a long time and to deliver the drug at a slow, controlled rate in order to exert its therapeutic effect for many hours. The compositions exemplified therein are either in the form of granules, granules filled in capsules, or tablets that break up into granules when subjected to the dissolution test specified in the Japanese Pharmacopoeia.
It is well accepted by those skilled in the art that granules are dissolved in a relatively shorter time than intact tablets because of their smaller size and increased surface area. Consequently, granules usually release drug in a shorter gastrointestinal transit time than intact tablets and are not well suited for a well-defined controlled drug delivery system. Thus, the composition disclosed in U.S. Pat. No. 4,777,033 which breaks up into granules does not provide the desired prolonged retention time at the site of absorption. A drug which is absorbed only from upper parts of the gastrointestinal tract would then be incompletely absorbed. Also, upon disintegration, a tablet yields a large number of granules and it is now recognized by those skilled in the art that multiparticulate systems, such as pellets or granules, are distributed over the length of the gastrointestinal tract releasing the drug at these different locations. Thus, the composition of U.S. Pat.. No. 4,777,033 may not release the drug specifically in the upper parts of the gastrointestinal tract. Additionally, it may be difficult to obtain the desired rate of release for a drug that has a high water solubility. The rapid release of a large quantity of such a highly soluble drug, i.e., a dose dumping effect, is particularly undesirable in controlled drug delivery systems because such formulations contain several times the amount of drug in a conventional formulation.
Japanese Patent No. 63-14715, assigned to Zeria Pharmaceutical Co., discloses a slow releasing pharmaceutical oral formulation comprising a high viscosity water soluble polymer, cross-linked insoluble polyvinylpyrrolidone, and a foaming component. The system is intended to release the drug slowly into the stomach. In the systems exemplified, the water soluble polymer includes cellulose derivatives or polyvinyl alcohol. For such systems sufficient quantities of water soluble polymers are required to prevent disintegration of the tablets into granules. Thus, when a high dose medicament is to be incorporated into tablets based on this system, the size of the tablets would be large.
U.S. Pat. No. 5,651,985, assigned to Bayer AG, discloses a composition comprising a pharmacologically active compound, a pharmaceutically acceptable auxiliary, polyvinylpyrrolidone, and a methacrylic acid polymer having an acidic number between 100 and 1200 mg of KOH/g of polymer solid substance. Optionally, the composition also contains a gas forming additive. The composition absorbs many times its weight of acidic water and forms a highly swollen gel of high mechanical and dimensional stability. The gel forming agent should be sufficient so that after administration it can swell up to a size which prevents passage through the pylorous for a relatively long time. At least 30% by weight and up to 90% by weight of the composition comprises the polymers, and thus dosage forms containing a high dose medicament would be large and inconvenient for oral administration.
Accordingly, none of the oral controlled drug delivery systems heretofore described is completely satisfactory.